Of recent years the plasmapheresis-type remedy has been applied to such autoimmune diseases as hyper-.gamma.-globulinemia, Goodpasture syndrome, chronic rheumatic disease, generalized lupus erythematosus, and hyperlipemia.
The object of the plasmapheresis-type remedy lies in the removal of high molecular proteins from the plasma existing in the immune complex or antibody, such as, for instance, anti-DNA antibody in generalized lupus erythematosus, anti-basement membrane antibody in Goodpasture syndrome, complex in immune complex nephritis, and anti-acetylcholine receptor antibody in bulbospinal paralysis. This method, however, involves weakness in that it requires the use of a large amount of human blood derivatives as the replacement transfusion to cover the plasma which has been separated and discarded. The replacement of as large quantity of plasma as possible is necessary for raising the efficacy of such plasmapheresis operation and it is said that 2.5 to 5.0 liter replacement is usually needed at a time. The operation requires so much albumin or fresh human plasma as mentioned in the above.
As a countermeasure, a trial is in practice with the operation in which the plasma, after having been separated from the blood through the first filtration membrane, is further led to the second filtration membrane where useful albumin (molecular weight about 68,000) is recovered while such high molecular proteins as immune complex, antibody immunoglobulin M (molecular weight about 900,000) hereinafter may be referred to as IgM), and immunoglobulin G (molecular weight about 160,000, hereinafter may be referred to as IgG).
For instance, it is disclosed in Trans. Amer. Soc Artif. Intern. Org., vol. 26, pp 406.about.409 (1980) and Medic. Instn. Jour., vol. 49, Suppl. pp 259.about.261 (1979) that a double filtration method can be practiced by combining the separation of blood with the use of a polyvinyl alcohol membrane and the separation of plasma components with the use of ethylene vinyl alcohol membrane. Also, Japanese Laid-Open Patent Publication No. 7258/83 discloses ultrafiltration purification of plasma achieved by use of a ultrafiltration membrane which can cut away high molecular substances whose molecular weight is more than one million. Japanese Laid-Open Patent Publication No. 175565/83 moreover discloses a plasmapheresis apparatus which is designed to remove high molecular proteins from the plasma by means of permeative separation in which the blood is made to permeate through a hollow fiber membrane from its membrane surface of lower fractional molecular weight to the surface of higher fractional molecular weight. As the concrete example of such a hollow fiber membrane, the disclosure refers to a hollow fiber, as seen under an electron microscope of 10,000 magnifications, having the inner surface covered with oval pores, each with average pore size of 0.68 .mu. in the fiber axis direction and 0.25 .mu. in the direction at right angle with the fiber axis and the outer surface likely covered with oval pores, each with average pore size of 0.4 .mu. in the fiber axis direction and 0.12 .mu. in the direction at right angle with the fiber axis. Another disclosure is made in Japanese Laid-Open Patent Publication No. 155865/83 of a hollow fiber membrane for plasmapheresis use comprising a skin layer, on at least one surface of the membrane, having micropores with average pore size of 50.about.450 .ANG. and a porous layer having micropores inside the membrane with average pore size of 500.about.1500 .ANG.. Another related disclosure is found in Artif. Org., vol. 13, No. 2, pp 931.about.934 (1984).
Those membranes mentioned above are, however, not always found to be satisfactory in practical use, since they do not necessarily satisfy every property required for carrying out plasmapheresis such as high albumin recovery removing IgM and IgG, and non-lowering of separation efficiency due to the clogging developed on the porous layer.